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Need Advice for Cassegrain 7" "project"

Started by RMachan, 12/29/2020 10:56PM
Posted 01/07/2021 12:47PM #10
Many thanks, great info.  I will post again after attempting alignment.  
Posted 01/16/2021 05:49PM | Edited 01/16/2021 05:50PM #11
Following with interest..... I would simply repeat something Ed touched on early on. Given the potential value of the scope if it turns out to not have any issues beyond the missing parts I would highly suggest not making any permanent modifications that would detract from that. Should it turn out to be a good performer with no appreciable optical flaws I would suggest then investing in the OEM parts to complete it which would be a relatively small investment in its overall value at resale.

Hope it works out well!
Greg

Dont Let Trump Cheat!! Demand Voter ID Now!
20" MidnighTelescopes f/5
8" f/16 Muffoletto Achro
Meade 6" AR6 f/8.0 Achro
Celestron C11
Parallax PI250 10" F/5 Newt
Vixen FL102S,NA140SS,R200SS
80mm Stellarvue Nighthawk with WO APOupgrade lens, 90mm f/16.67 Parallax Achro
LXD75/LX200, Mini-tower, GP-DX, CG5 ASGT, LXD650, GM-8, G11, GM-100, GM-150EX, GM-200 and a Gemini G40
4" portable AP convertable 44" or 70" pier
Stellarvue M7 Alt-Az, TSL7 Pier/Tripod
12.5" f/5 MidnighTelescopes DOB Swayze optics
Statham GA
Posted 01/16/2021 06:32PM #12
I believe you mentioned having or having access to a 3D printer.... Do you also have access to a lathe either your own or a friends? You might look into the approx length of the missing hardware (including the plate thickness in your calculations), print something along those lines and turn it down to a tight fit in the plate you mounted as well as gluing it in place once fitted. Alternatively a piece of PVC pipe might work as well. Before mounting it make sure you can fit up a diagonal (or make it long enough to compensate for not having a diagonal) or an eyepiece holder since this is just for testing purposes) 

I suspect since it was part of a testing apparatus there is a reasonably good chance it is optically sound....As long as you use good care in alignment you should be able to make things close enough to evaluate the optics. You may want to see if there is a astronomy club in your area as you may find someone willing to assist you regarding final adjustments regarding alignment of the optical train who already has the needed tools. 

I purposely wouldnt worry about a secondary focuser given the built in focusing ability if your only goal at this point is to test the optics before you spend the $$ for the OEM parts that are missing.

One question I have at this point would be does the plate you mounted on the back interfere with the primary mirror alignment screws? I didnt pay close attention to the pic. If so then you will want to drill some holes in that plate so you can still access them.

Dont Let Trump Cheat!! Demand Voter ID Now!
20" MidnighTelescopes f/5
8" f/16 Muffoletto Achro
Meade 6" AR6 f/8.0 Achro
Celestron C11
Parallax PI250 10" F/5 Newt
Vixen FL102S,NA140SS,R200SS
80mm Stellarvue Nighthawk with WO APOupgrade lens, 90mm f/16.67 Parallax Achro
LXD75/LX200, Mini-tower, GP-DX, CG5 ASGT, LXD650, GM-8, G11, GM-100, GM-150EX, GM-200 and a Gemini G40
4" portable AP convertable 44" or 70" pier
Stellarvue M7 Alt-Az, TSL7 Pier/Tripod
12.5" f/5 MidnighTelescopes DOB Swayze optics
Statham GA
Posted 01/16/2021 09:37PM #13
Thanks for your inputs Greg.  I have made a 3-D part that fits very well.  it was my test print in a gray plastic, the final will be a thicker, and in black for less reflected light.  I was going to post a photo.  Of what I have made, and I now also have an eyepiece and the diagonal.  I found that I made the piece long enough to bring it all into focus.  I have not gone out at night to look at some objects, but perhaps tonight.  If my camera can capture what I see from the eyepiece, I will post that as well.  Your comments are good.  The aluminum plate (which I reused from the original instrument) does not allow access to the adjustment of the primary mirror.  This is an excellent point, and when I re-print the final adapter plate in black, I will add these access holes.  It is easy to do.  It took me a bit of time to learn how to  do the 3-D cad, but the first print came out nearly perfect.  The focusing knob needs a bit more relief, but the rest was perfect. I strived for something between a slip fit and a press fit for the diagonal into my adapter plate, and the printer hit it on the nose.  I added a thumb screw, with an embedded nut that "could" have been used to tighten it up, but it was not needed at all.  It is actually a good alternative for the original hardware, but I agree with your point to not create any modifications to the telescope that would damage it.  The 3-D plate bolts onto the back of the telescope.  I just need to be careful that the bolts do not go in so far that they touch anything inside.  That will not be a problem with my second print, because I will make the plate the same thickness as the aluminum plate that was part of the prior instrument.  I just need to wait for a good viewing night to check everything out.  I suppose that I can also look at terrestrial objects, even during the daytime, if just looking for general performance, right?
Regards,
Roman
Posted 01/16/2021 09:39PM #14
Oh, and no access to a lathe, but the printer I have at home, so I work with what I have.  But I don't mind taking some time to learn a new skill (3-D cad drawings, for example).